It’s Friday, and time to lighten up for the weekend. So in honor of our favorite (work) day of the week, here are some fun facts to impress your date tonight — or, at the very least, your coworkers at the water cooler.

1. The first mechanical clock with hands was designed to imitate the path of a sundial shadow. In the Northern Hemisphere, where sundials were used for centuries, the shadow moves in a west to north to east rotation — which we now call clockwise.

2. Planck time is the name given to the smallest known unit of time. It is the time required for light to travel, in a vacuum, the distance of 1 Planck (0.0000000000000000000000000000000000000000001 second).

4. In 1905, Paris established “on demand” time over the phone. With a microphone transmitting the sound of ticking, a member of the Observatory staff counted minutes and seconds verbally on the line. This system was extremely popular, albeit time consuming.

5. Time on Earth is actually slowing down. Due to tidal friction from the sun and moon, the solar day is lengthening by 1.7 milliseconds each century as the Earth’s rotation slows down.